India's competition regulator on Tuesday fined three domestic airlines a combined 2.57 billion rupees ($39 million) for colluding to fix fuel surcharges for cargo transport.
Jet Airways, IndiGo, and SpiceJet were each hit with a penalty for "concerted action in fixing and revising Fuel Surcharge for transporting cargo", the Competition Commission of India said in a statement.
National carrier Air India and Go Airlines were also alleged to have been involved in anti-competitive practices in a complaint filed to the watchdog by the Express Industry Council of India, which represents couriers.
However, those two airlines were not penalised after the regulator said it found no evidence of collusion.
Jet Airways was handed the largest penalty of 1.5 billion rupees, IndiGo's parent company InterGlobe Aviation was fined 637 million rupees and budget carrier SpiceJet was fined 425 million rupees.
Indian airlines have struggled bitterly in recent years, losing a combined $10 billion since 2009, according to the Sydney-based Centre for Asia Pacific Aviation, while most are weighed down with debt.
The Commission said it had considered the "precarious financial position of airlines" in setting the penalties, which it said represented one percent of each airline's average turnover in the past three financial years.